Low-K dielectric functional imprinting materials

ABSTRACT

A polymerizable composition includes an organic modified silicate selected from the group consisting of silsesquioxanes having the composition RSiO 1.5 , partially condensed alkoxysilanes, organically modified silicates having the composition RSiO 3  and R 2 SiO 2 , and partially condensed orthosilicates having the composition SiOR 4 , where R is an organic substituent; a decomposable organic compound; a photoinitiator; and a release agent. The composition polymerizes upon exposure to UV radiation to form an inorganic silica network, and the decomposable organic compound decomposes upon exposure to heat to form pores in the inorganic silica network. The composition may be used to form a patterned dielectric layer in an integrated circuit device. A metallic film may be disposed on the patterned dielectric layer and then planarized.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/967,740, filed Oct. 18, 2004.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The United States government has a paid-up license in this invention andthe right in limited circumstance to require the patent owner to licenseothers on reasonable terms as provided by the terms of 70NANB4H3012awarded by National Institute of Standards (NIST) ATP Award.

BACKGROUND

The present invention relates to a method or material of fabricatingintegrated circuits, and in particular to a method of forming anintegrated circuit on a substrate having a low dielectric constant, aswell as a polymerizable composition for forming a patterned layer havinglow dielectric constant on a substrate.

There is a continuing desire in the microelectronics industry toincrease the circuit density in multilevel integrated circuit devices,e.g., memory and logic chips, thereby increasing their performance andreducing their cost. In order to accomplish this goal, it is alsodesirable to reduce the minimum feature size on the chip, e.g., circuitline width, and also to decrease the dielectric constant of theinterposed dielectric material to enable closer spacing of circuit lineswithout an increase in crosstalk and capacitive coupling. Further, thereis a desire to reduce the dielectric constant of the dielectricmaterials such as utilized in the back end of the line (BEOL) portion ofintegrated circuit devices, which contain input/output circuitry, toreduce the requisite drive current and power consumption for the device.

The most commonly used dielectric material in integrated circuits issilicon dioxide, which has a dielectric constant of about 4.0. Silicondioxide is readily grown or formed on the surface of a planar siliconwafer that is used to form the majority of the current semiconductordevices. Silicon dioxide has the requisite mechanical and thermalproperties to withstand processing operations and thermal cyclingassociated with semiconductor manufacturing. However, it is desired thatdielectric materials for future integrated circuit devices exhibit alower dielectric constant (e.g., <3.0) than exhibited by current silicondioxide. As inorganic materials have an inherent limitation todielectric constants of lower than about three, several types ofalternative materials have been developed to achieve lower dielectricconstants. A number of these alternative materials are organic polymers,which, if at least partially fluorinated, can have a dielectric constantof less than about three. However, the development of appropriateorganic polymers, as well as their depositions and patterning methods,poses significant challenges. The selection or choice of an organicmaterial is frequently limited by the need for higher temperature stepsin other aspects of the process, such as metallization or semiconductorfabrication. Another type of alternative material is an inorganicmaterial with dispersed micro voids or pores to achieve a lowereffective dielectric constant. Efforts to develop such materials aregenerally described in J. H. Golden, C. J. Hawker and P. S. Ho,“Designing Porous low-K Dielectrics,” Semiconductor International, May2001, which is incorporated herein by reference. Further, U.S. Pat. No.5,895,263, to Carter, et al., which is incorporated herein by reference,teaches a process for forming an integrated circuit device comprising(i) a substrate; (ii) metallic circuit lines positioned on the substrateand (iii) a dielectric material positioned on the circuit lines. Thedielectric material comprises porous organic modified polysilica.

Although porous inorganic materials can inherently withstand higherprocessing temperatures, like other dielectric materials, additionalchallenges arise due to the complexity of the patterning processes.Lithographic techniques are often employed in device micro fabrication.Traditionally, photolithography has been used to define or remove aportion of the dielectric material after it is deposited on thesubstrate. See S. Wolf et al., Silicon Processing for the VLSI Era,Volume 1—Process Technology, (1986), pp. 407-413, which is incorporatedherein by reference. Using microcircuit fabrication as an example, photoresist materials are applied to a dielectric material after depositionon a planar substrate. Next, the resist layer is selectively exposed toa form of radiation. An exposure tool and mask are often used to affectthe desired selective exposure. Patterns in the resist are formed whenthe dielectric layer undergoes a subsequent “developing” step. The areasof resist remaining after development protect the dielectric andsubstrate regions that they cover. Locations from which resist has beenremoved can be subjected to a variety of additive (e.g., lift-off) orsubtractive (e.g., etching) processes that transfer the pattern onto thesubstrate surface. However, photolithography has inherent sizelimitations that demand the use of shorter wavelength sources and moresophisticated optics to reduce the line width and feature sizes in themicro circuitry.

Thus in the process of U.S. Pat. No. 5,895,263 the low-K dielectriclayer must be first formed, and then patterned prior to deposition ofthe conductor material. The plurality of required processing stepsinherently increases the processing time, resulting in higher costs aswell as generally reduced product yield.

Further, as it is desirable to decrease the size of circuit features,that is line width and spacing between conductors, the alternativeinorganic materials must be capable of deposition with pore sizes thatare a fraction of the size of these features.

It is therefore a first object of the present invention to provide animproved method of fabricating an integrated circuit device comprising alow dielectric constant material between conductive lines and/or vias.

It is another object of the present invention to provide a process todeposit a patterned low dielectric constant inorganic material on aplanar substrate in a minimum number of process steps.

It is a further object of the invention to provide a robust, repeatableprocess for depositing a patterned low dielectric constant inorganicmaterial.

Other objects and advantages will be apparent from the followingdisclosure.

SUMMARY

In the present invention, the aforementioned objects are achieved bydeploying imprint lithography to mold a relief image corresponding tomicrocircuit features on a substantially planar substrate. The imprintmolding process deploys a polymerizable resin composition that issubsequently converted to a porous low dielectric constant inorganicmaterial.

The method of forming a relief image involves at least the steps ofcovering a substantially planar substrate with a polymerizable fluidcomposition; then contacting the polymerizable fluid composition with amold having a relief structure formed therein such that thepolymerizable fluid composition substantially fills the relief structurein the mold; subjecting the polymerizable fluid composition toconditions to polymerize the fluid composition and form a solidifiedpolymeric material there rom on the substrate; separating the mold fromthe solid polymeric material such that a replica of the relief structurein the mold is formed in the solidified polymeric material. Thepolymerizable composition is preferably a UV curable organic modifiedsilicate that comprises a decomposable organic component known as aporogen. Pores remain as the organic porogen decomposes during thesubsequent processing that converts the polymerized organic modifiedsilicate to an inorganic material.

As the UV curing is preferably conducted through a mold that is UVtransparent, another object of achieving a robust process for imprintingincludes using a UV curable polymerizable fluid that includes an organicmodified silicate, a decomposable organic compound, and afluorosurfactant to improve the release of the cured composition fromthe imprint-molding tool.

Other objects of the invention are achieved by using a process thatincludes the steps of providing a composition that includes a UV curableorganic modified silicate, a decomposable organic compound and asolvent; then spin coating the composition on a substrate, removing thesolvent, imprinting a circuit pattern in the remaining composition, UVcuring the remaining composition, heating the composition to condensethe organic modified silicate and decompose the decomposable polymer toform a porous patterned dielectric layer, and depositing metalconductors within the patterns formed in the porous dielectric material.

The above and other objects, effects, features, and advantages of thepresent invention will become more apparent from the followingdescription of the embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is schematic sectional elevation showing the mold with respect tothe substrate, as the first step in the process of imprinting a lowdielectric constant material.

FIG. 2 is schematic sectional elevation showing the disposition of thepolymerizable fluid between the mold and the substrate, as the next stepin the process of imprinting a low dielectric constant material.

FIG. 3 is schematic sectional elevation showing the polymerized fluiddisposed on the substrate after removal of the mold in a subsequent stepin the process of imprinting a low dielectric constant material.

FIG. 4 is schematic sectional elevation showing the polymerized materialdisposed on the substrate after conversion to a porous dielectricmaterial in a subsequent step in the process of imprinting a lowdielectric constant material.

FIG. 5 is schematic sectional elevation showing the conductive materialdeposited over the porous dielectric material in a subsequent step inthe process of forming a circuit.

FIG. 6 is schematic sectional elevation showing the circuit formed byplanarizing the conductive material deposited in the previous step.

FIG. 7 is schematic illustration of alternative methods for creating avariety of organically modified silicates that are optionally used toform the polymerizable fluid.

FIG. 8 is schematic illustration of the chemical reactions that occurduring the polymerization of the fluid and the subsequent conversion toa porous dielectric material in FIGS. 2, 3 and 4.

DETAILED DESCRIPTION

Referring to FIGS. 1 through 8, wherein like reference numerals refer tolike components in the various views, there is illustrated therein a newand improved circuit having a low dielectric constant, generallydenominated 100 herein.

Methods of imprinting to form a relief pattern are taught in U.S. Pat.No. 6,334,960, to Wilson, et al., the disclosure of which isincorporated herein by reference.

In the instant invention, the polymerizable material is a modifiedsilicate having organic functional groups that upon exposure to actinicradiation cross-link or react to form a non-fluid material replicatingthe shape of the mold. The cured or polymerized organic modifiedsilicate is subsequently, after removal of the mold, converted to aninorganic silicate upon thermal decomposition of the organic functionalgroups therein. The polymerizable material also contains one or morecomponents, which upon decomposition form pores or voids in theinorganic silicate. As shown in further detail in FIGS. 7 and 8, thepore forming material may be a separate component mixed, dissolved ordispersed on the polymerizable materials, or can also be chemicallybonding to the organic modified silicate. After conversion of thepolymerizable fluid to a solid that replicates the mold, one or moresteps are used to decompose the organic groups bound to the silicate andthe pore forming material, as well as to substantially complete theconversion to an inorganic silicate wherein water is condensed from theremaining hydroxyl group bound to silicon forming Si—O—Si linkages. Theprocess is carried out in a manner such that the silicate network formsaround the decomposing pore forming material, leaving nanometer scalevoids or pores behind. The polymerizable fluid composition may alsocomprise a diluent, and other materials employed in polymerizable fluidssuch as, but not limited, to catalysts and photo initiators, as will befurther described below with respect to preferred embodiments.

The mold used in the methods of the invention may be formed from variousconventional materials, such as, but not limited to, quartz, silicon,organic polymers, siloxane polymers, borosilicate glass, fluorocarbonpolymers, metal, and combinations of the above. Preferably, the materialis selected such that the mold is UV transparent, which allows thepolymerizable fluid composition covered by the mold to be exposed to anexternal radiation source. Thus, quartz molds are most preferred. Tofacilitate release of the mold from the solid polymeric material, themold may be treated with a surface modifying agent. Surface modifyingagents that may be employed include those that are known in the art. Anexample of a surface modifying agent is a fluorocarbon silylating agent.These surface modifying agents or release materials may be applied, forexample, from plasma sources, a Chemical Vapor Deposition method (CVD)such as analogs of the Parylene deposition process, or a treatmentinvolving deposition from a solution.

The methods of the invention will now be described in detail to theaccompanying drawing in which a preferred embodiment of the invention isshown. FIG. 1 illustrates the first step in the step-by-step sequencefor carrying out the method of the invention, which is depositing alow-k dielectric material and circuit pattern on a substrate 10. Asshown in FIG. 1, a UV transparent mold 30 is brought into proximity withsubstrate 10 such that gap 40 is formed between the bottom surface 31 ofmold 30 and substrate 10. Mold 30 has a nanoscale relief structureformed therein having an aspect ratio preferably ranging from about 0.1to about 10, and more preferably from about 0.5 to about 2.Specifically, the relief structures in the mold typically consist of aplurality of protrusions 41, each pair of which defines a recession 43therebetween. An exemplary width W₁ and depth d₁ of protrusions 41 andrecessions 43 may be from about 10 nm to about 5,000 microns. However,it should be understood that protrusions 41 and recessions 43 maycorrespond to virtually any feature.

Referring to FIG. 2, the polymerizable fluid composition preferably hasa low viscosity such that it may fill recessions 43 in an efficientmanner to form a contiguous layer of composition 50 over substrate 10.For example, the viscosity of composition 50 may range from about 0.01centipoises (cps) to about 100 cps measured at 25° C. and morepreferably from about 0.01 cps to about 5 cps measured at thistemperature. An exemplary technique for depositing composition 50employs depositing one or more spaced-apart discrete droplets (notshown) of composition 50 on substrate 10. Typically the droplets (notshown) are arranged in a pattern that minimizes trapping of gases whenthe droplets (not shown) of composition 50 merge to form a contiguouslayer over substrate 10 by interaction with mold 30, e.g., mechanicalcontact, electrical contact and the like. In an exemplary embodiment,droplets (not shown) of composition 50 are disposed on substrate 10.Contact between mold 30 and the droplets (not shown) is effectuated. Inresponse, composition 50 forms a contiguous layer over substrate 10. Itmay be desired to purge the region of substrate 10, for example, withhelium gas flowed at 5 pounds per square inch (psi), defined betweenmold 30 and both substrate 10 and droplets (not shown) before contactbetween mold 30 and composition 50 occurs. An exemplary purgingtechnique is disclosed in U.S. Pat. No. 7,090,716 to McMackin et al.,entitled SINGLE PHASE FLUID IMPRINT LITHOGRAPHY METHOD, which isincorporated by reference herein.

Alternatively, the polymerizable fluid can be first deposited as asubstantially uniform fluid layer on substrate 10 employing, forexample, spin-coating techniques. Thereafter mold 30 is brought to thesame proximity as shown in FIG. 2. In such cases, the fluid need nothave such a low viscosity, but the viscosity of the fluid should be lessthan about 200,000 cPs.

Further, to the extent that it is otherwise preferable to use differentcross-linkable organic polysilicates having higher molecular weight thanthe preferred oligomers, as described below, the mixture may contain asolvent as an inert diluent. The solvent may be selected to dissolve aparticular pore forming material as well as a fluorosurfactant(described in the more preferred embodiments below) or simply to lowerthe viscosity to a level low enough for spin coating on a planarsubstrate. After spin coating, the solvent is removed by vacuum orthermal evaporation, for example at about 100° C. for about 1 min. Thethen solvent free, planarized fluid can be directly imprinted bycontacting the mold thereto.

Suitable substrates for the device of the present invention comprisesilicon, silicon dioxide, glass, silicon nitride, ceramics, aluminum,copper and gallium arsenide. Other suitable substrates will be known tothose skilled in the art. In a multilayer integrated circuit device, anunderlying layer of insulated, planarized circuit lines can alsofunction as a substrate.

Referring now to FIG. 2, the polymerizable fluid composition 50 is thenexposed to conditions sufficient to polymerize the fluid. Preferably,the polymerizable fluid composition 50 is exposed to radiationsufficient to polymerize the fluid composition and form a solidifiedpolymeric material represented by 60 in FIG. 3. More specifically, thepolymerizable fluid composition is exposed to ultraviolet light,although other means for polymerizing the fluid may be employed such as,for example, heat or other forms of radiation. It should be understoodthat in some applications it might be desirable to use UV transparentsubstrates, in which case the exposure can be through the substrate, andin a further embodiment, the use of a mold that is opaque to UV light.

The selection of a method of initiating the polymerization of the fluidcomposition is known to one skilled in the art, and typically depends onthe specific application that is desired. Generally speaking, organicmodified polysilica is an oligomeric or polymeric compound comprisingsilicon, carbon, oxygen and hydrogen atoms. The polymerizable (orcrosslinkable) materials that may be used in the methods of theinvention may include various silicon-containing materials that areoften present themselves in the form of polymers or oligomers. Suitableorganic polysilica include (i) silsesquioxanes (ii) partially condensedalkoxysilanes (e.g., partially condensed by controlled hydrolysistetraethoxysilane having a number average molecular weight of about 500to 20,000); (iii) organically modified silicates having the compositionRSiO₂ and R₂SiO₂ wherein R is an organic substituent and (iv) partiallycondensed orthosilicates having the composition SiOR₄. Silsesquioxanesare polymeric silicate materials of the type RSiO_(1.5) where R is anorganic constituent. The silicon-containing material preferably containsthe element silicon in an amount greater than about 10 percent based onthe weight of the polymerizable fluid composition, and more preferably,greater than about 20 weight percent.

The silicon-containing polymerizable material also includes one or morependent functional groups from a variety that includes, as non-limitingexamples, epoxy groups, ketone groups, acetyl groups, vinyl groups,acrylate groups, methacrylate groups, and combinations of the above.Although not wishing to be bound by any theory, it is believed thatsuitable polymerizable fluid compositions may react according to avariety of reaction mechanisms such as, but not limited to, acidcatalysis, free radical polymerization, cationic polymerization, or 2+2photocycloaddition, and the like.

The most preferable forms of organic polysilica are of relatively lowmolecular weight, but predominantly have two or more pendent andreactive functional groups per molecule. Such organically modifiedsilicates are available under the trade name “ORMOCER” type resins andare available from Micro Resist Technology GmbH (Berlin, Germany).Typically, these materials are formed through the controlled hydrolysisand condensation of organically modified silanes, particularlyalkyltrialkoxysilanes, such as the mixture of molecules 710, 720, 730and 740 as illustrated in FIG. 7. As a non-limiting example for species720 R—Si (OX)₃, a traditional alkoxide precursor, X may represent, forexample, CH₃, CH₂H₅, CH₃H₇, and CH₄H₉. R may be any organic fragmentsuch as methyl, ethyl, propyl, butyl, isopropyl, aryl, phenyl, as wellas alkoxy (in which R is —(OX)). In molecule 730, W is preferably arylor phenyl. The proportions of molecules of the type 710, 720, 730 and740 may be modified to affect the molecular weight, extent ofcross-linking and glass transition temperature of the potentialresultant product species. A significant portion of the trialkoxysilanemore preferably has a reactive functional group, as in species 710,where R now terminates in a methacrylate group. Alternatively, R canterminate in an epoxide group, as for example species 740. It should beappreciated that R can also terminate in methacrylate, acrylate, vinyl,epoxide, and the like to provide a cross-linkable functionally that isactivated with UV light and the appropriate photo initiator and/orcatalyst. For either of 710 and 740, Z is optionally H, CH₃, CH₂H₅,CH₃H₇, C₄H₉ or a pore forming material P₂ or P₃. As used herein, theterm “ORMOCER” encompasses the foregoing materials as well as otherorganically modified ceramics, sometimes referred the trade namesORMACORE and ORMACLAD. It should be noted that for some portion of thecomposition, Si can alternatively be Ti, Zr, or Al to the extent it isdesirable to produce a mixed metal oxide material to provide otherproperties than a lower dielectric constant.

Upon the condensation reaction 700, the aforementioned trialkoxysilanereactants form various types of cross-linked networks with one or morereactive functional groups. Thus, upon the initial condensation reaction—OX groups are eliminated such that a Si—O— bonded network is formedhaving the generic structure illustrated as 750. The silicate portion ofthe network 750 is illustrated schematically as an oval for the otherspecies formed in condensation reaction 700. Depending on the exactcomposition and ratios of the initial reactants, polycondensationreaction 700 produces a variety of species having one of moremethacrylate, acrylate, vinyl, epoxide, and the like pendent functiongroups capable of cross-linking with each other either thermally or onexposure to actinic radiation with a suitable photo initiator and/orcatalyst. When R or Z is alternatively a porogen, designated P2 or P3wherein the above condensation reaction bonds the porogen pendent groupsto the Si—O— bonded network 750, as 755. P3 is intended to encompassstructures and molecules having an additional pendent methacrylate,acrylate, vinyl, epoxide, and the like pendent function groups capableof cross-linking. P2 and P3 thus can be oligomeric or polymeric, to varyor optimize the pore size and distribution. For example, trimethoxysilylnorbornene (TMSNB) and triethoxysilyl norbornene (TESNB) polymers(Promerus, Brecksville, Ohio) have been used as such chemically bondedporogens as described by Padovani, et al in “Chemically Bonded Porogensin Methylsilsesquioxane, I. Structure and Bonding,” Journal of theElectrochemical Society, 149 (12) F161-F170 (2002).), which isincorporated herein by reference. Alternatively, P1 or P2 can be poly(caprolactone) or other polyols of various molecular weights withpolyhydroxyl terminated or branched hydroxyl terminated speciespreferred to minimize the viscosity of the polymerizable fluid.

Thus, reaction 700 results in, among others, species 741, which has aSi—O— bonded network 750 with an epoxide pendent group, whereas otherproducts including species 744 which has a Si—O— bonded network 750 witha methacrylate pendent group. In contrast, as an alternative, species742 has Si—O— bonded network 750 with both an epoxide and a methacrylatependent group, while species 743 has a Si—O— bonded network 750 with twomethacrylate pendent groups. Another product of reaction 700 is species755 which has a Si—O— bonded network 750 with an epoxide, methacrylateand pore forming pendent group, P2. In species 760 the Si—O— bondednetwork 750 has both pendent epoxide and methacrylate groups as well asthe pore forming pendent group, P3, with P3 having the third pendentreactive group, that is methacrylate, bonded or pendent from it.

FIG. 8 illustrates the chemical reactions that occur during thepolymerization of the fluid 810 or 815 and the subsequent conversion toa porous dielectric material 835 or 840. Starting with the result ofreaction 700 provides a substantial number of compounds comprising aSi—O— bonded network 750 with two or more pendent reactive groupssuitable as the polymerizable fluid. It should be understood that theporogen, P1, could be present as a simple mixture that is either phaseseparated or dissolved in the polymerizable fluid. If the porogen isphase separated, it should be a stable emulsion with a particle size onthe scale of 3 to 50 nm. The mixture can include other species, such as841, a Si—O— bonded network 750 with an epoxide and two methacrylatependent groups. In an alternative species 860, two methacrylate groupsare pendent from the Si—O— bonded network 750, as well as a porogengroup P3 having an epoxide group pendent from it. In species 861, anepoxide group, methacrylate groups and porogen are pendent from theSi—O— bonded network 750. Thus, the polymerizable fluid includes theSi—O— bonded network 750 with pendent reactive groups and a porogenmaterial, bonded, dissolved or dispersed in the fluid.

Preferably, the subsequent polymerization step 815, wherein the fluid isexposed to actinic radiation with the mold in place, results in thesolid cross-linked resin 880. Thus, if the mixture contains epoxidegroups it is preferable to include a photo initiator that creates anacid such that the complete curing of a cross-linked network can beaccomplished in a single step, such that the mold can be rapidly removedand used to imprint other devices or portions of a substrate.

Alternatively, depending on the photo initiator, the subsequentcross-linking reaction 810 may initially occur via the methacrylategroups. This may be preferable if one wishes to increase the viscosityor partially cross-link the organic silicate precursors before a finalthermal cure process 820, which would cross-link any remaining epoxygroups, also forming a solid material having a three dimensioncross-linked network 880. When epoxide groups are present after theinitial exposure to actinic radiation, the curing can be accomplished inmultiple steps, using what is termed a soft bake at between 80 to 120°C. for 5 min. or less, followed by a higher temperature cure at betweenabout 120 to 240° C., for up to about 3 hrs.

The final step to decompose the organic modified silicate, to formporous silicate 70 in FIG. 4, preferably occurs under conditions thatheat the material to a temperature of about 425-450° C. for about 1 hourunder nitrogen. However, the decomposition process conditions can alsobe carried out in stages, depending on the differential temperaturedependence of the decomposition rates of the porogen as compared to theorganic modified silicate. However, whether the organic decompositionand elimination of the porogen is a one-step process 835 leading tofinal porous dielectric material 890, or take place in two steps,fundamentally the same reaction chemistry occurs in step 830 as organicgroups pendent on the silicon are decomposed. The organic modifiedsilicate contains some hydroxyl groups as a result of the partialpolycondensation reaction 700. The hydroxyl groups are represented inFIG. 8 by Si—OH. In the final step 840 at a higher temperature, water iscondensed from adjacent Si—OH groups forming a substantially inorganicsilica network. Simultaneously, the porogen P1, P2 or P3 materials thatare phase segregated decompose, forming nanometer scale pores,preferably having a diameter of about 3 to 30 nm or about one tenth ofthe feature size W₁ and d₁.

Referring back to FIG. 3, upon completion of the curing orpolymerization processes 815 or 810/820 described above, the mold 30 isremoved to leave the solidified polymeric material 60 deposited on thesubstrate 10. The patterned organic silicate coating has grooves 61surrounded by plateaus 62. As shown by FIG. 4 following either ofreactions 835 or 840 the resultant patterned polymeric material 60 isconverted to a substantially inorganic porous dielectric coating 70,that still includes groove 71 surrounded by plateaus 72, with a uniformdispersion of pores 81.

Another feature of the present invention is forming the dielectricmaterial, which is positioned over the circuit lines and/or between thecircuit lines and on the substrate. In multilevel integrated circuitdevices, the dielectric material is often planarized to function as asubstrate for lithographic formation of the next layer of circuit lines.The dielectric material comprises porous organic polysilicate.

Referring to FIG. 5, in the next step of the process for forming theintegrated circuit of the present invention, a metallic film 80 isdeposited onto the patterned dielectric layer 70. Preferred metallicmaterial is selected to provide suitable circuit lines and thuscomprises a metallic, electrically conductive material such as copper,tungsten, aluminum, silicides, gold, silver, or alloys thereof, and thelike. The metal is suitably deposited onto the patterned dielectriclayer by art known techniques such as chemical vapor deposition (CVD),plasma enhanced CVD, electro and electroless deposition, sputtering orthe like. Optionally, the circuit lines may be coated with a metallicliner such as a layer of nickel, tantalum or chromium or other layerssuch as barrier or adhesion layers (e.g., SiN, TiN).

Referring to FIG. 6, the last step of the process involves removal ofexcess metallic material (e.g., planarizing the metallic film 80) sothat the top of the metal filled grooves 91 are generally level with thetop of the patterned dielectric layer 72, resulting in integratedcircuit device 100. Device 100 generally comprises substrate 10,metallic circuit lines 90 and dielectric material 70. Planarization canbe accomplished using chemical/mechanical polishing or selective wet ordry etching. Suitable chemical/mechanical polishing techniques will beknown to those skilled in the art. In device 100, the interconnectedcircuit lines 90 function to distribute electrical signals in the deviceand to provide power input to and signal output from the device.Suitable integrated circuit devices will generally comprise multiplelayers of circuit lines, which are interconnected by vertical metallicstuds (not shown in the figure).

In the more preferred embodiments, the polymerizable composition alsoincludes a fluorosurfactant to improve the release properties andperformance life of the imprint mold or tool. A presently preferredfluorosurfactant is a non-ionic polymeric fluorochemical surfactant soldunder the trade name NOVEC FC-4432 by 3M Performance Materials Division(St. Paul, Minn.) Fluorosurfactant. An alternative fluorosurfacantincludes ZONYL FSO-100, available from DuPont Corporation (Wilmington,Del.).

In a preferred polymerizable fluid composition, percentage or fractiondecomposable polymer (porogen) to Si— is selected to produce a porevolume from about 10 to 40 volume %, and more preferably 20 to 30%,depending on the desired dielectric constant and the ultimate mechanicalstrength and durability required of the dielectric layer, it beingunderstood that even for nanoscale pores, increasing the total porositydecreases the strength and durability. The porogen component preferablycomprises from about 10 to 50 weight percent of the composition.Additionally it is preferable if the organic modified silicate comprisesat least about 10 weight percent silicon. More preferably, the organicmodified silicate has a molecular weight of less than about 50,000.Under such conditions, the polymerizable fluid composition preferablyhas viscosity of less than about 200,000 cPs.

EXAMPLE 1

As a theoretical example of a preferred composition for thepolymerizable fluid of the instant invention, 79.5 g ORMOCER b59 UVcurable organic modified silicate, 20 g TONE 0301 as the porogen and 0.5g FC4432 of fluorosurfactant are mixed together. As ORMOCER b59 isavailable from the manufacturer premixed with the appropriate photoinitiator the above composition can be used for imprint molding asdescribed above when exposed to UV radiation of a wavelength thatincludes 365 nm. “TONE” 0310 is a poly(caprolactone) polyol (CAS Reg.No. 37625-56-2) having a relatively low-melting point and istri-functional (3 —OH groups per molecule) with a number averagemolecular weight of about 900, and a hydroxyl number (mg KOH/g) of187.0, being available from the Dow Chemical Company (Midland, Mich.).Other polycaprolactones deemed suitable without undue experimentationinclude CAPA 3031, which is available from Solvay Caprolactones(Warrington, Cheshire, United Kingdom).

It is expected that the inventive process is susceptible to achievingthe smallest pore sizes, as the presence of the micro relief of the moldprior to the pore generation process minimizes the tendency for thenucleation and growth of larger pores.

It should be appreciated that one skilled in the art may select thesubstrate, mold, polymerizable fluid composition, surface modifyingagent, as well as any other materials such that the method of theinvention optimally functions according to the specific needs of the enduser.

While the invention has been described in connection with a preferredembodiment, it is not intended to limit the scope of the invention tothe particular form set forth, but on the contrary, it is intended tocover such alternatives, modifications, and equivalents as may be withinthe spirit and scope of the invention as defined by the appended claims.

What is claimed is:
 1. A polymerizable composition comprising: a) anorganic modified silicate selected from the group consisting ofsilsesquioxanes having the composition RSiO_(1.5), partially condensedalkoxysilanes, organically modified silicates having the compositionRSiO₃ and R₂SiO₂, and partially condensed orthosilicates having thecomposition SiOR₄, where each R is an organic substituent independentlycomprising (meth)acrylate, vinyl, or epoxide, and each partiallycondensed alkoxysilane comprises one or more pendant functional groupsindependently comprising (meth)acrylate, vinyl, or epoxide; b) adecomposable organic compound; c) a photoinitiator; and d) a releaseagent, wherein the composition polymerizes upon exposure to UV radiationto form an inorganic silica network, and the decomposable organiccompound decomposes upon exposure to heat to form pores in the inorganicsilica network.
 2. The composition of claim 1, wherein the organicmodified silicate has a molecular weight of less than about 50,000Dalton.
 3. The composition of claim 1, wherein the organic modifiedsilicate comprises at least 10 weight percent silicon.
 4. Thecomposition of claim 1, wherein the decomposable organic compound ischemically bonded to the UV curable organic modified silicate.
 5. Thecomposition of claim 1, wherein the decomposable organic compoundcomprises from about 10 to 50 weight percent of the composition.
 6. Thecomposition of claim 1, wherein the decomposable organic compound is apolycaprolactone.
 7. The composition of claim 1, wherein the releaseagent is a fluorosurfactant.
 8. The composition of claim 1, furthercomprising a solvent.
 9. The composition of claim 1, wherein a viscosityof the composition at 25° C. is in a range from about 0.01 centipoise toabout 100 centipoise.
 10. The composition of claim 1, wherein the poreshave a dimension of about 3 nm to about 30 nm.
 11. The composition ofclaim 1, wherein a volume of the pores in the inorganic silica networkis between about 10 vol % and about 40 vol %.
 12. The composition ofclaim 11, wherein the volume of the pores in the inorganic silicanetwork is between about 20 vol % and about 30 vol %.
 13. Thecomposition of claim 1, wherein the inorganic silica network is a bonded—Si—O— network.